THERE HAS BEEN so much hype about the Inner Harbor recently that news about disappointing attendance at the Columbus Center's new Hall of Exploration brings needed realism to the discussion of Baltimore's tourism potential. The mere fact that an attraction opens does not guarantee that it will meet visitor targets or can recoup set-up expenses.

With more than 48,000 visitors in its first four months, the Hall of Exploration did better than many established Baltimore City tourism attractions that also charge an admission fee. But Columbus Center officials were guilty of overly ambitious attendance projections. As a result, the center is now in default on its $6 million bank loan and is scrambling to restructure its finances.

This crunch, however painful for the $160 million marine research and education complex, may have some healthy long-term consequences.

Among them is the possibility of closer cooperation with the Nation-al Aquarium, the Inner Harbor's No. 1 tourist attraction that draws 1.6 million visitors each year.

Last weekend, the National Aquarium for the first time offered visitors the option of buying a discount combination ticket that included the Columbus Center's Hall of Exploration. Some 13 percent of visitors reportedly took advantage of the deal. Other joint ventures are possible.

"It is no secret we are talking at various levels," reports aquarium director David M. Pittenger. "We are just investigating. No specific decisions have been reached."

One of the Columbus Center's problems from the very beginning has been a name that gives no hint about the varied activities inside. A similar vagueness plagues the Hall of Exploration name.

Another problem has been Columbus Center officials' assumption that the proximity of the National Aquarium translates into instant success. Clearly this is not the case; the Hall of Exploration has to be able to attract visitors solely on the basis of its exhibits.

Given more time and better marketing, the Columbus Center's Hall of Exploration should be able to develop into a major tourist draw.

But the Columbus Center will always be doomed to play second fiddle to the booming aquarium -- unless the two become part of an Inner Harbor powerhouse.